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Engagement
Author: mistertee
Date Created: 19 Oct 2015 8:36 PM
Views: 121
Likes: 0
Comments: 5
  • raspberrypi_dart_urr_
  • tmp36_dualanalogueradiotransmitter_universalradioreceiver_urr
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Remote temperature monitoring

mistertee
mistertee
19 Oct 2015

This post shows how to use the Dual Analogue Radio Transmitter (DART) and the Universal Radio Receiver (URR) to monitor the temperature of one or more freezer.

 

The DART collects data from 2 analogue inputs and transmits this to a receiver using a 433 MHz FM radio module. (FM radio modules gives gives significantly better range and noise performance when compared to AM modules). More information on the DART and URR can be found here.

 

 

 

 

The TMP36 is very easy to use. The relationship between the temperature and analogue voltage output is as follows:

 

Temp (in deg C) = voltage (in mv) divided by 10  minus 50

 

So for example if the TMP36 output volts was 800 mV the temperature would be 800/10 = 80 mnus 50 would be 30 deg C.

 

 

 

The DART has 2 sets of screw terminals. The TMP36 temperature sesnor can be connected directlty to these. The timing of the temperature measurement and transmission can be set to 1 every minute or 1 every 10 minutes.

 

 

On this project uses 2 TMP36 devices. One is connected directlty to the screw terminals and the other is on a cable of approximately 1 metre in length. The TMP36 at the end of this is housed in a plastic tube for protection.

 

 

 

  The image below shows the DART in pace with one of the TMP36 device inside the freezer and one outside. This way we can monitor the temperature inside and outside the freezer (which in this case is in the garage).

 

 

 

 

The Universal Radio REceiver is connected to a Raspberry Pi, using A Custard Pi 1A breakout board. (This has easy connection points and also has 0.1A fuses on the 5V and 3.3V rails to prevent too much current being drawn from the RPi.)

 

 

 

 

 

 

 

The Python code to receive the data on the serial port is listedat the end of this post. Please read this document for more comprehensive instructions on using the UART on the Raspberry Pi.

 

The data displayed on the HDMI monitor connected to the Raspberry Pi is hsown here.

 

The data is received every minute and is interpreted as follows.

 

1st digit = device type )always 1 for a DART)

2nd digit = address set on this DART

3rd digit = data count (goes from 0 to 15 and then starts again. Each data set is sent twice)

4th digit = temp 1 = -21 deg C (inside the freezer)

5th digit = temp 2 = 12 deg C (in the garage)

6th digit = batt voltage = 4.417 V

 

PROJECT IDEA #1: Send an e-mail from the Raspberry Pi if the temperature inside the freezer rises by 5 degrees.

 

PROJECT IDEA #2: Log the temperature from a number of freezers for food hygiene purposes. (One URR can receive data from a number of DART devices).

 

Summary: The DART and URR devices allow remote temperature monitoring to be set up very quickly.

 

Appendix: Python code to recive and display data from the serial port.

 

#!/usr/bin/env python

 

import time

import serial

 

ser = serial.Serial(

 

    port='/dev/ttyAMA0',

    baudrate = 9600,

    parity=serial.PARITY_NONE,

    stopbits=serial.STOPBITS_ONE,

    bytesize=serial.EIGHTBITS,

    timeout=0

 

)

 

ser.flushInput()

while True:

    data1 = ser.read(1)

    data2 = ser.read(1)

    data3 = ser.read(1)

    data4 = ser.read(1)

    data5 = ser.read(1)

    data6 = ser.read(1)

  

    if len(data1) >0:

        localtime = time.asctime( time.localtime(time.time()))

        print localtime

        temp1 = (1024*ord(data4)/2550)-50

        temp2 = (1024*ord(data5)/2550)-50

        battv =  (1024 * ord(data6) * 11)/255

        print ord(data2), ord(data3), ord(data1),

        print "Temp1 = ", temp1,

        print "Temp2 = ", temp2,

        print "BattV", battv   

   

    time.sleep (0.5)

 

 

ser.close()

Anonymous

Top Comments

  • michaelkellett
    michaelkellett over 6 years ago +2

    I don't see a CE mark (or any reference to WEE) on the DART or its documentation - did I miss them or do they not exist ?

     

    MK

  • michaelkellett
    michaelkellett over 6 years ago in reply to mistertee +1

    Good - I asked because I couldn't see them on the pictures. Your stuff is  a lot more expensive than similar little boards from unknown sources in China via Ebay or Aliexpress (which generally are not…

  • mistertee
    mistertee over 6 years ago in reply to michaelkellett

    Hi Michael, I spent a lot of time evaluating the modules from Aliexpress. They are cheap but AM only and gave me a range of only 10 meters or so through a brick wall. Also AM is more prone to blocking in the presence of noise compared to FM. These FM modules are costlier but give line of sight range in excess of 200 meters with a 1/4 wave antennae. I couldn't find any FM modules on Aliexpress.

     

    The modules from Aliexpress are just radio modules. They don't have any of the "gubbins" necessary for reliable RF transmission like Manchester Coding and pre-amble to condition the detection thresholds. Without this you would be lucky to get a range of even 10 meters line of sight even with FM modules.

     

    The 2 key things that drove me to this design was range and power consumption - I was keen to have a solution that could work off batteries for more than 1 year. The quiescent power consumption with the DART module is around 25 uA. With data transmissions every 1 minute, I estimate battery life easily in excess of 1 year.

     

    I did consider wi-fi but the issues that kept me from using them were range and power consumption. The other consideration was that w-fi solutione are aimed at the "mass market" and soon there will be modules from Aliexpress with a $1 price tag driving the DART out of the market. I was keen to produce a "niche" product with superior range performance that had some longevity.

     

    Thanks for your input.

    MrT

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  • michaelkellett
    michaelkellett over 6 years ago in reply to mistertee

    Good - I asked because I couldn't see them on the pictures. Your stuff is  a lot more expensive than similar little boards from unknown sources in China via Ebay or Aliexpress (which generally are not marked) and obviously your compliance with the rules helps make up for that.

     

    Have you though about doing a Wifi based TX based on the ESP8266 - it would be nice to buy one that complied with regulations.

    The nice thing is that it wouldn't need an RX board on the computer end and would work with Pis and everything else.

     

    MK

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  • mistertee
    mistertee over 6 years ago in reply to michaelkellett

    Hi MK,

    The DART (&URR) is CE marked and carries the Wheelie bin symbol. If you are interested it complies with the RoHS regulations as well (this is covered by the CE mark).  Did you have a particular application in mind?

    MrT

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  • gadget.iom
    gadget.iom over 6 years ago in reply to michaelkellett

    Michael Kellett wrote:

     

    I don't see a CE mark (or any reference to WEE) on the DART or its documentation - did I miss them or do they not exist ?

     

    MK

    Good point!

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  • michaelkellett
    michaelkellett over 6 years ago

    I don't see a CE mark (or any reference to WEE) on the DART or its documentation - did I miss them or do they not exist ?

     

    MK

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